162 MANUAL OF VEGETABLE-GARDEN INSECTS 



the female and occurs in two forms, one with normal functional 

 wings and the other with abbreviated wings. The fly deposits 

 her small, white, oblong eggs, about ^iir ii^ch in length, on the 

 surface of the potato. The eggs hatch in five or six days and 

 the young maggot works its way into the tuber, usually taking 

 advantage of a scab spot or other injury. The maggots attack 

 the healthy tissue and under favorable conditions of tempera- 

 ture and moisture will continue their work generation after 

 generation until the tuber is completely destroyed. The mag- 

 gots become mature in about a week and then transform to 

 delicate white pupae in flimsy silken cocoons either in the soil 

 or on the surface of the tuber. The adults emerge in three or 

 four days. From twenty to twenty-five days are required for 

 the insect to complete its life cycle. 



Control. 



Serious injury by the potato scab gnat is of rare occurrence. 

 Only uninfested seed potatoes should be planted and land on 

 which the crop has been infected should not be used for potatoes 

 the following year. Potatoes grown in dry, light soil are not 

 likely to be attacked. 



References 



W. Va. Agr. Exp. Sta. Sp. Bull. 2, pp. 97-111. 1895. 

 Hopkins, Proc. Ent. Soc. Wash., 3, pp. 149-159. 1895. 



The Potato Tuber Moth 



Phthorimoea cperculella Zeller 



Potatoes in California and Texas are subject to attack by 

 a small whitish caterpillar about ^ inch in length that riddles 

 the tubers w^th burrows, causing them to decay. The potato 

 tuber moth is also a troublesome tobacco pest and when feeding 

 on this plant is known as the split-worm or tobacco leaf-miner. 



